U.S. patent number 9,057,378 [Application Number 13/653,709] was granted by the patent office on 2015-06-16 for intelligent air moving apparatus.
This patent grant is currently assigned to Hewlett-Packard Development Company, L.P.. The grantee listed for this patent is HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P.. Invention is credited to John P. Franz, David F. Heinrich, Stephen A. Kay, Thomas D. Rhodes, Wade D. Vinson.
United States Patent |
9,057,378 |
Franz , et al. |
June 16, 2015 |
Intelligent air moving apparatus
Abstract
An intelligent air moving apparatus for cooling an electronics
enclosure includes a motor for driving a fan at a variable
rotational speed and a microcontroller for controlling the
rotational speed of the motor. The microcontroller includes a speed
sensor for sensing the rotational speed such that when the sensed
rotational speed deviates below a target speed, the microcontroller
detects a locked rotor condition.
Inventors: |
Franz; John P. (Houston,
TX), Vinson; Wade D. (Magnolia, TX), Rhodes; Thomas
D. (The Woodlands, TX), Heinrich; David F. (Tomball,
TX), Kay; Stephen A. (Tomball, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. |
Houston |
TX |
US |
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Assignee: |
Hewlett-Packard Development
Company, L.P. (Houston, TX)
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Family
ID: |
40132514 |
Appl.
No.: |
13/653,709 |
Filed: |
October 17, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130037250 A1 |
Feb 14, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12107140 |
Apr 22, 2008 |
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60943679 |
Jun 13, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D
27/008 (20130101); F04D 27/004 (20130101); G06F
1/20 (20130101); H05K 7/20209 (20130101); F05D
2270/335 (20130101); Y02B 30/70 (20130101) |
Current International
Class: |
F04D
27/00 (20060101); G06F 1/20 (20060101); H05K
7/20 (20060101) |
Field of
Search: |
;417/18,22,32,44.1,44.11,45,63 ;700/282 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
US. Appl. No. 13/243,369, Examiner's Answer mailed on Jun. 21,
2013, 23 pages. cited by applicant .
U.S. Appl. No. 13/243,369, Final Office Action mailed Mar. 4, 2013,
19 pages. cited by applicant .
U.S. Appl. No. 13/243,369, Non-Final Office Action mailed Aug. 6,
2012, 13 pages. cited by applicant.
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Primary Examiner: Freay; Charles
Assistant Examiner: Stimpert; Philip
Attorney, Agent or Firm: Hewlett-Packard Patent
Department
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser.
No. 12/107,140, filed Apr. 22, 2008, entitled "Intelligent Air
Moving Apparatus" and claims priority of U.S. Provisional
Application No. 60/943,679, filed Jun. 13, 2007, entitled
"Intelligent High Performance Air Mover." The content of the
related applications are incorporated herein by reference in their
entirety.
Claims
What is claimed is:
1. A method of cooling an electronics enclosure comprising:
providing at least one fan module, the fan module comprising a
multi-phase motor for driving a fan at a variable rotational speed
and a microcontroller for controlling the rotational speed of the
motor; sensing the rotational speed; detecting with the
microcontroller a locked rotor event when the sensed rotational
speed falls below a target speed by at least a threshold amount;
and providing an alert to indicate recommended inspection of the
fan in response to a predetermined plurality of shut down and
restart sequences.
2. The method of claim 1, further comprising: controlling, with the
microcontroller, the rotational speed to be outside one or more
speed avoidance zones defined by natural frequencies of the fan
module.
3. The method of claim 1, further comprising: when more than one
fan module is provided, starting the fans in each of the at least
one fan modules sequentially instead of simultaneously to avoid
power surges.
4. The method of claim 1, further comprising: providing a
communications interface adapted to receive a target speed signal;
and maintaining the rotational speed at a default speed when the
communications interface detects a loss of the target speed
signal.
5. A method of cooling an electronics enclosure comprising:
providing a plurality of fan modules, each fan module including: a
multi-phase motor for driving a fan at a variable rotational speed,
a microcontroller for controlling a rotational speed of the motor
based on a measured rotational speed of the motor and a predefined
target speed, and an interface that connects each of the plurality
of fan modules to a centralized infrastructure controller external
to the fan module, the interface enables communication between the
microcontroller and the centralized infrastructure controller such
that the microcontroller autonomously controls the cooling of the
fan module; determining with the microcontroller, the measured
rotational speed; optimizing performance of each of the plurality
of fan modules using the microcontroller contained within the fan
module, the microcontroller compares the measured rotational speed
and the predefined target speed stored on the microcontroller; and
starting the fans in each of the at least one fan modules
sequentially instead of simultaneously to avoid power surges; and
providing an alert to indicate recommended inspection of the fan in
response to a predetermined plurality of shut down and restart
sequences.
6. The method of claim 5, wherein optimizing performance comprises:
adjusting a control signal from the microcontroller to the
multi-phase motor.
7. The method of claim 5, further comprising: limiting
communication with the centralized infrastructure controller.
8. The method of claim 5, further comprising: performing
computational tasks with the microcontroller of the fan module.
9. The method of claim 5, further comprising: storing in memory of
the fan module at least one data value comprising a speed avoidance
zone.
10. The method of claim 5, further comprising: controlling, with
the microcontroller, the rotational speed to be outside one or more
speed avoidance zones defined by natural frequencies of the fan
module; and maintaining the rotational speed at a default speed
when the communications interface detects a loss of a target speed
signal.
11. The method of claim 5, further comprising: detecting with the
microcontroller a locked rotor event when the measured rotational
speed falls below the predefined target speed by at least a
threshold amount.
12. A method of cooling an electronics enclosure comprising:
providing a plurality of fan modules, each fan module including: a
multi-phase motor for driving a fan at a variable rotational speed,
a microcontroller for controlling a rotational speed of the motor
based on a measured rotational speed of the motor and a predefined
target speed, an interface that connects each of the plurality of
fan modules to a centralized infrastructure controller external to
the fan module, the interface enables communication between the
microcontroller and the centralized infrastructure controller, and
a memory connected to the microcontroller and the interface to
store data received therefrom; determining with the
microcontroller, the measured rotational speed; managing
performance of each of the plurality of fan modules using the
microcontroller contained within the fan module, the
microcontroller compares the measured rotational speed and the
predefined target speed stored on the microcontroller such that the
microcontroller autonomously controls the cooling of the fan module
using data stored in the memory; measuring a fan air inlet
temperature; automatically shutting down rotation of the fan
modules in response to the fan air inlet temperature indicating a
visual thermal event; and providing an alert to indicate
recommended inspection of the fan in response to a predetermined
plurality of shut down and restart sequences.
13. The method of claim 12, wherein managing performance comprises
sensing a drop in voltage indicative of removal of power from the
multi-phase motor and, based on the sensed drop in voltage,
simultaneously energizing all one or more motor phases to stop the
motor from rotating.
14. The method of claim 12, further comprising performing
computational tasks with the microcontroller of the fan module.
15. The method of claim 12, further comprising: receiving the
predefined target speed from the infrastructure controller; and
storing the predefined target speed in the memory.
16. The method of claim 12, further comprising: starting the fans
in each of the at least one fan modules sequentially to avoid power
surges.
17. The method of claim 12, wherein managing performance comprises
detecting with the microcontroller a locked rotor event when the
measured rotational speed falls below the predefined target speed
by at least a threshold amount.
18. The method of claim 2, wherein the one or more speed avoidance
zones are stored and accessed by the microcontroller.
19. The method of claim 1, further comprising sensing a drop in
voltage indicative of removal of power from the multi-phase motor
and, based on the sensed drop in voltage, simultaneously energizing
all one or more motor phases to stop the motor from rotating.
Description
BACKGROUND
Fans powered by electric motors are commonly used to cool computer
servers and other electronic equipment within an electronics
enclosure. Existing electronics enclosure cooling fans have limited
intelligence and provide little or no communication to an
infrastructure controller capable of monitoring the electronics
systems the fans are designed to cool. Therefore, existing fans
lack the ability to be optimized for thermal performance, noise,
power consumption, reliability, maintenance and warranty costs, and
other relevant parameters.
In typical computing systems, including computer servers, multiple
fans are required to maintain sufficient airflow to cool the
electronics equipment within the enclosure. Further, the multiple
fans must be able to operate effectively and harmoniously in
conjunction with each other. Therefore, limited intelligence fans
require substantial amounts of computational overhead to ensure the
fans are operating to provide adequate cooling, and to detect fan
failures before the electronics equipment overheats.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate embodiments of an intelligent
air moving apparatus as described herein.
In the drawings:
FIG 1 shows a schematic view of a fan module interconnected to an
infrastructure controller.
FIG 2 shows an electronics enclosure having a plurality of fan
modules mounted thereto for providing cooling.
DETAILED DESCRIPTION
There is shown in FIG 1 an air moving apparatus 100 comprising a
fan module 10 interconnected to an infrastructure controller 50.
The infrastructure controller 50 is further interconnected to an
electronics enclosure 60 to monitor various operational parameters
including temperature of the electronics enclosure 60. The fan
module 10 comprises a fan 12, a microcontroller 20, and an
interface 40. The fan 12 has a motor 14 adapted to drive a fan
blade 16 at a variable rotational speed, as commanded by the
microcontroller 20, to accommodate the cooling needs of the
electronics enclosure 60. The microcontroller 20 controls the speed
of the motor 16 and includes a speed sensor 30 to sense the motor
rotational speed and to provide a feedback signal of the actual
motor speed. The microcontroller can additionally include other
sensors, such as a voltage sensor 34, and a current sensor 36. In
an embodiment, the microcontroller 20 receives instructions from
the infrastructure controller 50 and sends fan status information
to the infrastructure controller 50 via the interface 40.
The microcontroller 20 can be a microprocessor. Alternatively, the
microcontroller functions can be performed by solid state
components or other circuitry. An exemplary microcontroller is
commonly known as a Programmable Interface Controller or
Programmable Intelligent Computer ("PIC"), an inexpensive
chip-based programmable microcontroller. The term "PIC" is used
interchangeably with the term "microcontroller" in this
application. The microcontroller 20 includes a memory 28 for
storing data.
The microcontroller 20 includes features to allow the fan module 10
to assess its own status. The microcontroller 20 further is adapted
to communicate information regarding operation of the fan module 10
to the infrastructure controller 50 to facilitate efficient and
quiet cooling provided by the fan 12 to the electronics equipment
60. The microcontroller 20 can reduce power consumption and noise
generation by the fan module 10, and can increase reliability of
the fan 12, optimizing the fan 12 to operate at a level adequate to
ensure adequate cooling of the electronics equipment 60 rather than
having to operate at a margin of safety above such a level.
Precise Speed Control.
In order to optimize fan module performance, the microcontroller 20
includes a feedback control loop and a speed control algorithm for
precisely regulating the rotational speed of the motor 14. In one
embodiment, a DC motor is used and motor speed is controlled by
pulse-width modulation (PWM). The speed is controlled to a target
speed that can be a preprogrammed speed, a speed setpoint received
from the infrastructure controller 50, or a default speed at which
the fan motor 14 operates in the event of a communication failure
between the infrastructure controller 50 and the fan module 10. The
default speed can be the most recent target speed received from the
infrastructure controller 50 or a preset default speed stored in
the memory 28 of the microcontroller 20. The control loop detects
the actual rotational speed of the motor 14 as measured or sensed
by the speed sensor 30 and the algorithm compares the actual speed
to the target speed. The motor rotational speed can be measured
periodically over various time spans depending on the accuracy of
control required. When the measured speed of the motor 14 deviates
from the target speed by at least a preset tolerance, the algorithm
adjusts the control signal to the motor 14 to cause the actual
motor speed to approach the target speed. Accurate speed control is
used to improve power usage and reliability by causing a fan motor
14 to operate only as fast as necessary to achieve the required
cooling.
Speed control can also be accomplished by using a temperature
sensor 80 measuring fan inlet air temperature changes that may be
caused by changes to the ambient conditions of the room or loading
of the electronic equipment in the enclosure. A target speed can be
set based on the fan inlet temperature detected by the temperature
sensor 80. In one example, if the ambient temperature becomes too
high (e.g., the room air conditioning fails), the fan can
accelerate to a higher speed as required. In another example, if an
electrical short causes a visual thermal event (i.e., a fire), the
fan can shut down and allow the event to extinguish itself (since
most materials in the electronics enclosure are rated to stop
burning) rather than aggravating the fire by providing additional
air.
In one embodiment, an external crystal oscillator is used to ensure
an accurate time base for motor speed measurements. The speed
control algorithm can contain optimizations to handle large changes
in motor speed settings by attempting to estimate the correct PWM
setting for a given motor speed, thereby achieving the target speed
faster by making fewer incremental steps. Optimization of the speed
control algorithm is particularly useful in the event that the
motor speed or target speed changes by a large amount in a short
period of time.
Avoidance of Natural and Beat Frequencies.
Providing precise speed control of the motor 14 enables the fan
module 10 to avoid natural vibration frequencies. All devices with
rotating components, including the fan 12 and fan module 10, have
natural vibration frequencies at certain speeds, and often these
speeds fall within the range of normal operation. If the device is
operated at such speeds, the natural vibration frequencies can
cause not only vibrations but also acoustic noise. These natural
vibration frequencies can be readily determined, either by
theoretical or empirical methods, and correlated with motor speeds,
based at least in part on the characteristics of the motor 14, the
fan blade 16, and the fan module 10. In an embodiment, speed
avoidance data is stored in tables in the memory 28 of the
microcontroller 20. The data tables (generally expressed in RPM)
establish speed avoidance zones within a predetermined band around
each of the natural vibration frequencies. The speed avoidance zone
data can be stored in the microcontroller 20 or can be communicated
to the microcontroller 20 from the infrastructure controller 50.
The microcontroller 20 does not permit the fan 12 to operate within
any of the speed avoidance zones. Instead, when cooling
requirements call for a speed within a speed avoidance zone, the
microcontroller 20 sends the fan motor 14 a speed setpoint that is
slightly above or below the prohibited zone, in order to maintain
sufficient cooling flow while minimizing power used by the motor
14. The speed setpoint can be outside the avoidance zone by a
percentage of the target speed or by a fixed number of RPM,
depending on the characteristics of the fan. In one embodiment, the
microcontroller 20 controls the fan motor 14 to operate at a speed
approximately 100 RPM above or below the speed avoidance zone.
A system 100 may comprise two or more fan modules 10 operating in
conjunction to cool an electronics enclosure 60, as shown in FIG 2.
Whenever two similarly sized fans 12 operate nearby each other at
similar speeds, there is a potential for beat frequencies to occur.
As an extension of the speed avoidance tables, additional speed
avoidance zones can be created to avoid such beat frequencies. As
with the individual speed avoidance zones, when a target speed is
provided to a microcontroller 20 to operate a fan 12 in one of the
beat frequency speed avoidance zones, the microcontroller 20
automatically adjusts the rotational speed of the fan 12 to be
slightly above the prohibited range in order to prevent unwanted
tone resonance and beat frequencies while still achieving at least
the minimum speed required to provide proper cooling.
Locked Rotor Protection.
In one embodiment, the fan motor 14 is a conventional DC motor
having a stator and a rotor, wherein the fan blade 16 spins along
with the rotor while the stator remains stationary with respect to
the remainder of the fan 12. If the rotor locks up, the fan blade
16 will not spin and the fan 12 will not be able to deliver
cooling. Additionally, a locked rotor can damage the fan 12. There
are at least four possible types of locked rotor events that
prevent the fan 12 from rotating when it is instructed to rotate by
the microcontroller 20: lock-up at startup, lock-up while running
at constant speed, lock-up during speed changes, and partial
lock-up that creates a drag but does not completely stop the fan
blade from spinning. Typically, these events occur when the fan
blade 16 is blocked from running due to loose cables or other
objects obstructing the fan 12 in one way or another, or due to
debris or wear in the bearings of the motor 14.
Some fans in the industry use Hall effect sensors (which sense
proper commutation of the motor) to detect situations when a fan is
commanded to run but the fan blade or impeller is not spinning as
it should. However, in an embodiment in which the fan module 10 is
packaged into a very small volume, there is insufficient space for
Hall effect sensors. In other embodiments, it may be
cost-prohibitive to use Hall effect sensors. Therefore, in order to
detect a locked rotor event, the microcontroller 20 employs a speed
sensor 30 capable of detecting back electromotive force voltage
(back EMF) and correlating the back EMF with fan speed. When the
back EMF sensor 30 detects a locked rotor event based on back EMF,
a failure alert is generated by the microcontroller 20 and a motor
restart sequence is initiated. In an embodiment, the
microcontroller 20 is a PIC and this functionality is accomplished
by code on the PIC, combined with hardware circuitry. In another
embodiment, the microcontroller 20 uses hardware circuitry
alone.
Back EMF voltages are tabulated or stored in the memory 28 of the
microcontroller 20 for known operating conditions when the fan 12
is operating normally, so they can be compared with voltages
measured at various actual operating conditions to detect whether
the actual operating conditions have deviated by at least a
threshold amount outside normal ranges. The threshold amount can be
specified as a percentage of the target speed or as a fixed number
of RPM. If such a deviation is detected by the speed sensor 30, a
comparator in the microcontroller 20 triggers a restart of the
motor 14. Alternatively, the microcontroller 20 can sample the back
EMF voltages detected by the speed sensor 30 and code can be used
to determine whether the voltage value is normal or abnormal. If
abnormal, the microcontroller 20 can instruct the motor 14 to shut
down and restart.
In one embodiment, the time to detect a locked rotor condition is
dependent upon the target speed of the fan 12, ranging from about 1
second at a high target speed to about 6 seconds at a low target
speed. During a shut down and restart, the fan 12 is turned off for
about 7 seconds and takes an additional 3-4 seconds to restart. To
prevent overheating of the motor 14, the number of restart cycles
can be limited, and an alert created when the limit is reached to
indicate that the fan 12 needs inspection and/or replacement.
Speed Brake.
Rotating devices such as cooling fans can be dangerous to
maintenance or repair personnel. In particular, high performance
cooling fans such as the fan 12 can operate at speeds of 18,000 RPM
or higher. Therefore, the fan 12 is provided with an electronic
speed brake to stop the fan blade 16 from rotating within about one
second after when power is removed from the motor 14 or the module
10 is removed, thereby significantly reducing the chance that a
service person, tool, or other object will contact rotating fan
blades during servicing and/or removal of the fan 12 and/or the fan
module 10. The electronic speed brake functions as follows. After
power is removed from the motor 14, the voltage sensor 34 senses or
detects a corresponding voltage drop indicative of the removal of
power. When a predetermined threshold drop in voltage is reached,
the microcontroller 20 simultaneously energizes all motor phases,
causing the sequenced commutation to stop substantially immediately
and thus substantially immediately stopping the fan blades from
rotating.
Autonomous Operation.
In one embodiment, the fan module 10 operates autonomously and has
intelligence keep the fan 12 running to cool the system even when
the microcontroller 20 does not receive a target speed signal from
the infrastructure controller 50. Once the fan 12 has been
instructed to operate at a rotational speed or RPM setpoint, the
fan module 10, through the microcontroller 20 or PIC, is capable of
controlling and monitoring its own performance. Therefore, the fan
module 10 will maintain the speed of the fan 12 at a target speed.
The target speed can be provided by the infrastructure controller
50 or can be stored in the memory 28 of the microcontroller 20.
If the fan 12 is unable to reach or maintain the target speed, the
microcontroller 20 communicates an alert signal to the
infrastructure controller 50. By having this intelligence built
into the fan module 10 as opposed to being centralized in the
infrastructure controller 50, the fan 12 can operate to cool the
electronics enclosure 60 if the infrastructure controller 50 is not
operating or if the fan module 10 loses communication with the
infrastructure controller 50. Also, because some electronics
enclosures 60 have ten or more cooling fan modules 10, intelligence
built into the fan module 10 reduces the computational loading on
the infrastructure controller 50.
Sequenced and Gradual Startup.
In a system 100 including multiple fan modules 10, starting two or
more fans 12 simultaneously at a desired setpoint speed could
result in undesirable power surges. To avoid such power surges, the
microcontroller 20 can implement various strategies. In one
embodiment, the fans 12 can be started up sequentially. In another
embodiment, the fans 12 can be started up at a relatively low speed
and then gradually ramped up to the setpoint speed. In yet another
embodiment, the fans 12 can be started up sequentially at a
relatively low speed and then each fan gradually ramped up to the
setpoint speed.
Fan Failure Indicator.
The fan module 10 can include at least one colored light emitting
diode (LED) to indicate status conditions of the fan 12. In an
embodiment, a green LED 22 and an amber LED 24 are connected to the
microcontroller 20. When the fan module 10 is off, i.e., no power
is being delivered to the fan 12 and the microcontroller 20 has not
been instructed to operate the fan 12, neither LED 22, 24 is
illuminated. When power is on and the fan 12 is operating normally,
i.e., within a preset range of a target speed, the green LED 22 is
illuminated. The present range can be bounded by a percentage of
the target speed or by a number of RPM above and/or below the
target speed, and can be provided by the infrastructure controller
50 or stored in the memory 28 of the microcontroller 20. When the
fan 12 fails to operate, the amber LED 24 is illuminated. Circuitry
is included to keep the LED 24 illuminated amber in the event of
loss of programming to the microcontroller 20 or corrupted
microcontroller memory 28 to help distinguish and diagnose this
failure scenario. When an error condition is present that does not
prevent the fan 12 from operating, the amber LED 24 blinks. Error
conditions can include, but are not limited to, the fan module 10
being installed in an incorrect location, a loss of communication
from the infrastructure controller 50 to the fan module 10 (i.e.,
to the microcontroller 20), and receipt of an override signal.
Blinking the amber LED 24 to indicate such conditions helps to
diagnose problems prior to an indication from the infrastructure
controller 50 of a more serious condition, such as insufficient
cooling being provided to the electronics enclosure 60.
Because the microcontroller 20 has the ability to measure both
speed of the motor 14 and power drawn by the motor 14, a
pre-failure alert can be provided when the microcontroller 20
detects a deviation from the expected relationship between fan
speed and power. Such a deviation could be due to bearing wear,
debris build-up at the fan inlet, or other conditions requiring
attention. Similarly, one or more temperature sensors 80 can be
used on the motor 14 to detect deviations from expected normal
operating temperatures that can be indicative of impending motor
failure.
Interactive Communication.
In one embodiment, the interface 40 is a bi-directional interface
through which the fan module 10 can exchange communications with
the infrastructure controller 50 via a primary communication link
70. Through the interface 40, the microcontroller 20 communicates
operational and other information to enable optimization of fan
performance or diagnosis of problems within the fan module 10 in
the event of an error condition or failure. The infrastructure
controller 50 can instruct the microcontroller 20 to operate the
fan 12 at a target rotational speed. Further, the infrastructure
controller 50 can read status parameters of the fan 12, as
collected by the microcontroller 20 through its various sensors,
such as the motor speed and the voltage and current being supplied
to the motor 14. The infrastructure controller 50 can also read
static and dynamic data stored in the memory 28 of the
microcontroller 20. Static data can include identifying information
such as spare part numbers, serial numbers, and date of
manufacture, as well as operational information such as power-on
speed and override PWM setting. Dynamic data can include
information such as total hours of motor operation, total
revolutions of motor operation, and logged failures or error events
(e.g., locked rotor restarts). The infrastructure controller 50 can
update the stored data to affect operation of the fan 12, for
example to update the speed zone avoidance data and overall speed
range settings.
Power Circuit and Overcurrent Protector.
The microcontroller 20 includes a power sensing circuit 38 to
measure the power being consumed by the fan 12, thereby enabling
the infrastructure controller 50 to monitor and effectively
allocate power to the various fan modules 10. The power circuit 38
computes power based on measurements from the voltage sensor 34 and
the current sensor 36, and reports dynamic power consumption to the
infrastructure controller 50, which tracks power allocation. In
addition the power circuit 38 can be used to monitor for impending
failures due to bearing wear in the fan motor 14, i.e., to provide
a pre-failure notification when the motor 14 is drawing more power
than it should for a specified rotational speed.
Conventional power circuits use a "one time" fuse that blows if a
threshold current is exceeded. When such a fuse blows, any
equipment powered through that fuse ceases to function until the
fuse is replaced. In the disclosed embodiment, the power sensing
circuit 38 monitors power levels. If the power circuit 38
determines that current being drawn by the fan module 10 is too
close to a predetermined shutdown threshold, an overcurrent
protector 39 shuts off power while preventing damage to itself. The
microcontroller 20 is then able to reset and restart the fan 12,
avoiding the need for hardware repair resulting from a high current
condition.
Redundant Communication Channels.
In one embodiment, the interface 40 in the fan module 10 uses a bus
architecture to provide a communication link 70 to the
infrastructure controller 50. In particular, an I2C bus may be
used. If the communication link 70 is broken, an alternate signal
path 75 is provided from the interface 40 to the infrastructure
controller 50. Thus, in the event that the infrastructure
controller 50 and interface 40 cannot communicate with one another,
the infrastructure controller 50 automatically switches over to the
alternate signal path and causes the microcontroller 20 to perform
a self diagnostic recovery reset, which in most cases will restore
the bus communication link 70 from the infrastructure controller 50
to the interface 40.
As shown in the embodiment illustrated in FIG 2, a system 100
comprising three fan modules 10 is provided. Any number of fan
modules 10 can be provided in a system 100. Because each fan module
10 has an independent microcontroller 20, the fans 12 can be
individually controlled to allow fine cooling control and to avoid
large current surges caused by changing power states on all fans 12
simultaneously. An infrastructure controller 50 provides control
signals to each fan module 10. The fan modules 10 are supplied with
48 VDC and the speed of each fan motor 14 is controlled by a
pulse-width modulated (PWM) 5 VDC signal operating at 20 kHz. The
speed sensor 30 in each fan module 10 produces a tachometer signal
which is used by the microcontroller 20 to determine rotational
speed, and cooling capacity can be inferred from the tachometer
signal based on the speed versus airflow characteristics of the fan
blade 16. In an embodiment, the tachometer signal is produced as an
open collector square wave signal four times per revolution of the
fan motor 14. If no control signal is received by a particular fan
module 10, that module 10 instructs the fan 12 to spin at a default
speed. The default speed can be stored in the memory 28 of the
microcontroller 20 or can be the most recent target speed provided
by the infrastructure controller 50. Each microcontroller 20
generates a fault signal if any one of a number of "error"
conditions occurs, and the fault signal is communicated to the
infrastructure controller 50 through an interface 40 in the fan
module 10.
When installed, each fan module 10 drives a presence signal low, so
that if the fan module 10 loses connection with the infrastructure
controller 50, the presence signal will go high and the
infrastructure controller will be alerted. Each fan module 10
preferably carries in the memory 28 of the microcontroller 20 a
unique identifying information (e.g., model and serial numbers) to
facilitate tracking of individual fan modules 10. Each fan module
memory 28 also records operating characteristics of the fan 12 and
stores pre-failure warranty information.
* * * * *